1. Technical Field
The present invention relates to a process to create at least one stand-off on an electronic circuit.
2. Discussion of Related Art
Although not exclusively reserved therefore, this process is more particularly applicable to the known "flip chip" technology wherein several high density electronic chips are assembled onto a printed circuit board by means of so-called "stand-off's". A stand-off is a metallic stud or bump which, additionally to interconnecting the chip to the board, creates a distance between them. This distance is necessary to reduce fatigue effects in the interconnection due to differences in temperature expansion coefficients of the chip, generally constituted by silicon, and the carrier, i.e. the printed circuit board. The stud may obviously not collapse, especially during the assembly process.
Processes to create stand-offs or studs on a chip are already known in the art, e.g. from an IBM.TM. technology called "Controlled Collapsed Chip Connection" or "C4" technology. Therein, the studs are made using evaporation techniques through molybdenum masks. This known technology involves relatively expensive silicon back-end processing and, additionally, requires high cost mask material. A method for electrically connecting flip chips to a printed circuit substrate is for instance disclosed in the U.S. Pat. No. 5,261,593 of Nov. 16, 1993, and an apparatus therefore is disclosed in the U.S. Pat. No. 5,349,500 of Sep. 20, 1994.
In the known technologies, the stand-offs are realized on the chips, i.e. by the chip providers. Since several different chips are generally mounted on a same printed circuit board, the masks for the processing of these chips need to be created for relatively low production volumes. Furthermore, at least parts of these "bumping" processes are repeated by the different chip providers. All these elements lead to increase the production cost of the flip chip technology.